Screw pump is a rotary pump that relies on the volume change and movement of the meshing space formed by the pump body and screw to transport liquid or pressurize it. Screw pumps are divided into single screw pumps, double screw pumps, and triple screw pumps based on the number of screws. When the active screw rotates, it drives the driven screw that engages with it to rotate together, and the meshing space volume of the screw at one end of the suction chamber gradually increases, while the pressure decreases. The liquid enters the meshing space volume under the pressure difference. When the volume reaches its maximum and a sealing chamber is formed, the liquid continuously moves axially in each sealing chamber until it is discharged from one end of the chamber. At this point, the meshing space volume of the screw at one end of the discharge chamber gradually decreases, and the liquid is discharged. The working principle of a screw pump is similar to that of a gear pump, except that the screw replaces the gear in structure. The table shows the characteristics and application range of various screw pumps. The flow rate and pressure pulse of the screw pump are very small, and the noise and vibration are small. It has self suction ability, but screw processing is more difficult. There are two types of pumps: single suction and double suction, but single screw pumps only have single suction. The pump must be equipped with a safety valve (single screw pumps do not need to be equipped) to prevent damage to the pump or prime mover due to certain reasons such as blockage of the discharge pipe, which causes the outlet pressure of the pump to exceed the allowable value.